Balloon altitude control using density adjustment and/or volume adjustment

ABSTRACT

A balloon having an envelope and a payload positioned beneath the envelope. The envelope comprises a first portion and a second portion, wherein the first portion allows more solar energy to be transferred to gas within the envelope than the second portion. The balloon may operate in a first mode in which altitudinal movement of the balloon is caused, at least in part, by rotating the envelope to change an amount of the first portion that faces the sun and an amount of the second portion that faces the sun, and wherein the control system is further configured to cause the balloon to operate in a second mode in which altitudinal movement of the balloon is caused, at least in part, by moving a lifting gas or air into or out of the envelope.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable.

SUMMARY

In one aspect, a balloon is provided. The balloon includes: (a) anenvelope, (b) a payload positioned beneath the envelope, wherein theenvelope comprises a first portion and a second portion, wherein thefirst portion allows more solar energy to be transferred to the gaswithin the envelope than and the second portion, and (c) a controlsystem that is configured to cause the balloon to operate using a firstmode in which altitudinal movement of the balloon is caused, at least inpart, by rotating the envelope to change an amount of the first portionthat faces the sun and an amount of the second portion that faces thesun, wherein the control system is further configured to cause theballoon to operate in a second mode in which altitudinal movement of theballoon is caused, at least in part, by moving a lifting gas or air intoor out of the envelope. The envelope may be is non-symmetrical in shapesuch that the first portion has a surface area that is greater than asurface area of the second portion, wherein more solar energy istransferred to gas within the envelope when the first portion of theballoon is facing the sun than when the second portion of the balloon isfacing the sun. Alternately, or additionally the first portion of theenvelope may have different reflective, transmissive, and/or emissiveproperties than the second portion, including in the thermal IR.

In another aspect, a computer-implemented method involves: (a) causing aballoon to operate using a first mode, wherein the balloon comprises anenvelope and a payload positioned beneath the envelope, wherein theenvelope comprises a first portion and a second portion, wherein thefirst portion allows more solar energy to be transferred to the gaswithin the envelope than the second portion, and wherein operation usingthe first mode comprises causing altitudinal movement of the balloon viarotation of the envelope to change an amount of the first portion thatfaces the sun and an amount of the second portion that faces the sun;(b) determining that an ambient light level is below a threshold; and(c) responsively causing the balloon to operate using a second mode,wherein operation in the second mode comprises causing altitudinalmovement of the balloon via movement of a lifting gas or air into or outof the envelope.

In another aspect, a non-transitory computer readable medium has storedtherein instructions that are executable by a computing device to causethe computing device to perform functions comprising: (a) causing aballoon to operate using a first mode, wherein the balloon comprises anenvelope and a payload positioned beneath the envelope, wherein theenvelope comprises a first portion and a second portion, wherein thefirst portion allows more solar energy to be transferred to the gaswithin the envelope than the second portion, and wherein operation usingthe first mode comprises causing altitudinal movement of the balloon viarotation of the envelope to change an amount of the first portion thatfaces the sun and an amount of the second portion that faces the sun;(b) determining that an ambient light level is below a threshold; and(c) responsively causing the balloon to operate using a second mode,wherein operation in the second mode comprises causing altitudinalmovement of the balloon via movement of a lifting gas or air into or outof the envelope.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a balloon network,according to an example embodiment.

FIG. 2 is a block diagram illustrating a balloon-network control system,according to an example embodiment.

FIG. 3 is a simplified block diagram illustrating a high-altitudeballoon, according to an example embodiment.

FIG. 4 shows a balloon network that includes super-nodes and sub-nodes,according to an example embodiment.

FIG. 5A shows a balloon, according to an example embodiment.

FIG. 5B shows a top view of the balloon shown in FIG. 5A.

FIGS. 6A and 6B shows the balloon of FIGS. 5A and 5B with certainportions of the balloon envelope exposed to the sun.

FIG. 7 shows a balloon, according to an example embodiment.

FIG. 8A shows a front view of a balloon, according to an exampleembodiment and FIG. 8B shows a side view of the balloon shown in FIG.8A.

FIG. 9 is a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodimentor feature described herein is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the Figures should notbe viewed as limiting. It should be understood that other embodimentsmay include more or less of each element shown in a given Figure.Further, some of the illustrated elements may be combined or omitted.Yet further, an example embodiment may include elements that are notillustrated in the Figures.

1. Overview

Example embodiments help to provide a data network that includes aplurality of balloons; for example, a mesh network formed byhigh-altitude balloons deployed in the stratosphere. Since winds in thestratosphere may affect the locations of the balloons in a differentialmanner, each balloon in an example network may be configured to changeits horizontal position by adjusting its vertical position (i.e.,altitude). For instance, by adjusting its altitude, a balloon may beable find winds that will carry it horizontally (e.g., latitudinallyand/or longitudinally) to a desired horizontal location.

Further, in an example balloon network, the balloons may communicatewith one another using free-space optical communications. For instance,the balloons may be configured for optical communications usingultra-bright LEDs (which are also referred to as “high-power” or“high-output” LEDs). In some instances, lasers could be used instead ofor in addition to LEDs, although regulations for laser communicationsmay restrict laser usage. In addition, the balloons may communicate withground-based station(s) using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.That is, the balloons in a high-altitude-balloon network could besubstantially similar to each other in one or more ways. Morespecifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with one or more other balloons viafree-space optical links. Further, some or all of the balloons in such anetwork, may additionally be configured to communicate with ground-basedand/or satellite-based station(s) using RF and/or opticalcommunications. Thus, in some embodiments, the balloons may behomogenous in so far as each balloon is configured for free-spaceoptical communication with other balloons, but heterogeneous with regardto RF communications with ground-based stations.

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons. For example, some balloons in a heterogeneous network may beconfigured as super-nodes, while other balloons may be configured assub-nodes. It is also possible that some balloons in a heterogeneousnetwork may be configured to function as both a super-node and asub-node. Such balloons may function as either a super-node or asub-node at a particular time, or, alternatively, act as bothsimultaneously depending on the context. For instance, an exampleballoon could aggregate search requests of a first type to transmit to aground-based station. The example balloon could also send searchrequests of a second type to another balloon, which could act as asuper-node in that context. Further, some balloons, which may besuper-nodes in an example embodiment, can be configured to communicatevia optical links with ground-based stations and/or satellites.

In an example configuration, the super-node balloons may be configuredto communicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for someother type of communication, such as RF communications. In that case, asuper-node may be further configured to communicate with sub-nodes usingRF communications. Thus, the sub-nodes may relay communications betweenthe super-nodes and one or more ground-based stations using RFcommunications. In this way, the super-nodes may collectively functionas backhaul for the balloon network, while the sub-nodes function torelay communications from the super-nodes to ground-based stations

In the present disclosed embodiments, the altitude of a balloon may becontrolled in a number of different ways. For example, the buoyancy, andthus the altitude, of the balloon may be controlled by adjusting thetemperature of the gas within an envelope of the balloon. It should bepointed out that the temperature of the gas within the envelope itselfdoes not change the buoyancy of the balloon. In order for temperature tochange buoyancy, the envelope needs to be somewhat elastic so that itexpands when heated, or the gas inside is heated, or conversely that itcollapses to some degree when cooled, since it is the density change ofthe gas within the balloon that, by definition, is what changes thebuoyancy of the balloon. In any event, under proper circumstances, thealtitude of balloon may be controlled by increasing or decreasing thetemperature of the gas within the envelope. Thus, during the daylighthours, it may be possible to control the altitude of the balloon bycontrolling the density of the gas within the balloon, by controllingthe amount of solar energy that is absorbed by the gas.

In addition, when the sun goes down, the gas within the envelope of theballoon may cool quickly, and controlling the altitude of the balloon byadjusting the temperature of the gas within the envelope may not bepossible. Therefore, at night, it may be desirable to pump more or lessgas into the envelope of the balloon, or into a bladder within theenvelope of the balloon, to increase or decrease the buoyancy of theballoon. Therefore, it may be useful to provide altitude control for aballoon during the day using a first mode of operation by controllingthe density of the gas within the envelope of the balloon through thecontrol of the temperature of the gas within the envelope of theballoon, and it be also be useful to control the altitude of the balloonat night using a second mode of operation by adjusting the volume of thegas within the balloon envelope or bladder to adjust the buoyancy of theballoon as appropriate. At certain times it may be desirable to use bothgas density (through controlling gas temperature) and gas volume (bypumping gas into or out of the balloon envelope or bladder) to controlthe altitude of the balloon. Therefore, it may be desirable to providealtitude control using either the first mode of operation or the secondmode of operation, or using the first mode and second mode of operationat the same time.

During the daytime, when the sun is present, the temperature of the gaswithin the envelope may be controlled by controlling the amount of solarenergy that is absorbed by the gas within the balloon envelope. Tocontrol the amount of solar energy that is absorbed by the gas withinthe balloon envelope, the absorptive/reflective properties of thesurface of the balloon envelope may be adjusted, or varied, by providinga balloon with an envelope having a first portion of the envelope havinga property different from a second portion of the envelope, with respectto reflecting or absorbing solar energy.

In an example embodiment, a first portion of the envelope may be coloredwhite, or some other light color, which reflects more solar energy thana dark colored surface to help prevent the temperature of the gas withinthe envelope from rising. A second portion of the envelope could becolored black, or some other dark color, which absorbs more solar energythan a lightly colored surface to allow more solar energy to be absorbedby the gas within the envelope, causing the temperature of the gaswithin the envelope to rise. It may also be the case that a clear sidewould allow the sun to penetrate into the balloon, warming the airinside. In this way a clear surface would be equivalent to the darkcolored or black surface for the portion of the envelope that ispresented towards the sun when it desired to warm up the air inside theballoon (relative to the light colored or otherwise reflective side).

Alternately, or in addition to varying the absorptive or reflectiveproperties of the portions of the balloon envelope to control the amountof solar energy entering the balloon envelope, it is also possible toprovide a non-symmetrically shaped balloon such that a first portion ofthe balloon may be oriented towards the sun that allows for more solarenergy to be absorbed by the gas within the envelope than when a secondportion of the balloon is oriented towards the sun. Therefore, bychoosing which side of the non-symmetrically shaped balloon envelope toorient towards the sun, differential heat may be brought into theballoon. By rotating or turning the balloon relative to the sun (whichworks to the extent the sun is not directly overhead), substantialheating or cooling may be caused by presenting more or less of thesurface of the envelope to the sun independent of the one or morematerials used on the portions on the outside of the balloon. Of course,a non-symmetrically shaped balloon may be used with a balloon having thesame material used for its entire envelope surface area, or may be usedin conjunction with a first portion of the balloon having differentreflective, transmissive, or emissive properties than a second portionof the balloon.

Thus, the balloon envelope may be engineered to serve as an orientablesolar thermal energy collection system. When it is desired to obtain orcollect more solar thermal energy the portion of the balloon that allowsfor the most transmission or absorption of solar energy may be rotatedand oriented towards the sun. It should also be noted that the materialschosen to make this envelope might look very different in the thermal IRvs. the visible band. Thus, it may be useful to characterize or describethe material used for the first portion of the balloon and the secondportion of the balloon in terms of their reflectivity, transmissivity,and emissivity properties in the two bands (thermal IR and visibleband), as well as for each side, since the properties may be quitedifferent. For example, envelope material that looks white to human eyesmight in fact be quite black (low R (reflectivity), high E (emissivity),low T (transmissivity) when viewed in the thermal IR. Likewise, amaterial that appears very reflective on both sides (high R) when viewedin the visible band may have very different properties on one side vs.the other when viewed in the thermal IR band, e.g. metalized Mylar whichlooks like R=0.95 E=0.05/Rir=0.9 Eir=0.1 on the metalized side and R=0.9E=0.1/Rir=0.5 Eir=0.5 on the polymer side.

By controlling which portion of the balloon envelope is facing the sun,the temperature of the gas within the balloon envelope may becontrolled. In an example embodiment, the balloon may be equipped withthe ability to rotate the balloon envelope so that the first portion ofthe envelope or the second portion of the envelope is positioned facingthe sun. Where it is desired to increase the altitude of balloon, thefirst portion of the balloon envelope that allows for more solar energyto be absorbed by the gas within the envelope may be positioned facingthe sun to increase the temperature of the gas within envelope (andincrease the altitude of the balloon). Similarly, where it is desired todecrease the altitude of balloon, the second portion of the envelopethat allows for less solar energy to be absorbed by the gas within theballoon envelope may be positioned facing the sun to decrease thetemperature of the gas within the balloon envelope (and decrease thealtitude of the balloon). Relying on solar heat to raise and lower theballoon may not be the most reliable way to accomplish the goal ofstation keeping of the balloon. However, the use of solar energy has theadvantage that it is very energy efficient and doesn't take much energy.Specifically, it takes less energy to turn the balloon into a desiredposition relative to the sun (using many of the possible ways of turningthe balloon) than to change altitude by some other means such as byrunning an electric air compressor. Thus, the use of solar energy tocontrol balloon altitude may advantageously use less energy than othermethods of controlling balloon altitude.

At night time, when the sun is down, it may no longer be possible to usedirect solar energy rotation of the balloon envelope to control thealtitude of the balloon. Therefore, alternate means for controllingaltitude should be available during the night. A second mode ofoperation that may be used to control the altitude of the balloon may beby introducing additional lifting gas into the balloon envelope orbladder. In this manner, gas may be pumped into or out of the balloonenvelope or bladder to control the altitude of the balloon at night.Altimeters or other devices may be used determine the altitude and/orrate of descent and provide for switching from a first mode of altitudecontrol using solar energy, to a second mode of altitude control usinginflation/deflation of the balloon envelope or bladder with gas, or somecombination thereof.

Furthermore, the payload may include one or more solar cells to storeenergy that can be used for altitude control during the night. Forexample, solar energy stored during the day may be used to control thealtitude of the balloon by pumping gas into, or out of, the envelope ofthe balloon, or the bladder of the balloon. Of course, the stored solarenergy could also be used to store energy used for rotating the balloonenvelope during the day time.

As another example, the solar energy stored during the day may be usedto heat the gas within the balloon envelope to provide increasedbuoyancy. Where hydrogen is used as the lifting gas, it may be possibleto use the cooperative operation of a solar array and a fuel cell.Operation of the fuel cell generates ballast (water, a byproduct of thefuel cell reaction) whose mass can be controlled by controlling theoperation of the fuel cell. Fuel for the fuel cell can be generated byoxidizing hydrogen, supported by energy from the solar cells. Hydrogengas may be burned at night to heat the payload and/or the gas within theballoon envelope and/or bladder.

2. Example Balloon Networks

FIG. 1 is a simplified block diagram illustrating a balloon network 100,according to an example embodiment. As shown, balloon network 100includes balloons 102A to 102F, which are configured to communicate withone another via free-space optical links 104. Balloons 102A to 102Fcould additionally or alternatively be configured to communicate withone another via RF links 114. Balloons 102A to 102F may collectivelyfunction as a mesh network for packet-data communications. Further, atleast some of balloons 102A and 102B may be configured for RFcommunications with ground-based stations 106 and 112 via respective RFlinks 108. Further, some balloons, such as balloon 102F, could beconfigured to communicate via optical link 110 with ground-based station112.

In an example embodiment, balloons 102A to 102F are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In an exampleembodiment, high-altitude balloons may be generally configured tooperate in an altitude range within the stratosphere that has relativelylow wind speed (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102F may generally be configured to operate at altitudes between 18 kmand 25 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has relatively low wind speeds (e.g., windsbetween 5 and 20 mph) and relatively little turbulence. Further, whilethe winds between 18 km and 25 km may vary with latitude and by season,the variations can be modeled in a reasonably accurate manner.Additionally, altitudes above 18 km are typically above the maximumflight level designated for commercial air traffic. Therefore,interference with commercial flights is not a concern when balloons aredeployed between 18 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may beconfigured to transmit an optical signal via an optical link 104. In anexample embodiment, a given balloon 102A to 102F may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102F may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,in order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102F may include one or moreoptical receivers. Additional details of example balloons are discussedin greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more ofvarious different RF air-interface protocols for communication withground-based stations 106 and 112 via respective RF links 108. Forinstance, some or all of balloons 102A to 102F may be configured tocommunicate with ground-based stations 106 and 112 using protocolsdescribed in IEEE 802.11 (including any of the IEEE 802.11 revisions),various cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/orLTE, and/or one or more propriety protocols developed for balloon-groundRF communication, among other possibilities.

In a further aspect, there may be scenarios where RF links 108 do notprovide a desired link capacity for balloon-to-ground communications.For instance, increased capacity may be desirable to provide backhaullinks from a ground-based gateway, and in other scenarios as well.Accordingly, an example network may also include downlink balloons,which could provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F is configured as adownlink balloon. Like other balloons in an example network, a downlinkballoon 102F may be operable for optical communication with otherballoons via optical links 104. However, a downlink balloon 102F mayalso be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and the ground-based station 112.

Note that in some implementations, a downlink balloon 102F mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102F may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102F, anexample balloon network can also include multiple downlink balloons. Onthe other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of, or in addition to, afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which may provide an RF link with substantially the same capacity as oneof the optical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 112, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order to communicate with a balloon 102A to 102F over an RF link 108.As such, ground-based stations 106 and 112 may be configured as anaccess point via which various devices can connect to balloon network100. Ground-based stations 106 and 112 may have other configurationsand/or serve other purposes without departing from the scope of theinvention.

In a further aspect, some or all of balloons 102A to 102F could beconfigured to establish a communication link with space-based satellitesin addition to, or as an alternative to, a ground-based communicationlink. In some embodiments, a balloon may communicate with a satellitevia an optical link. However, other types of satellite communicationsare possible.

Further, some ground-based stations, such as ground-based stations 106and 112, may be configured as gateways between balloon network 100 andone or more other networks. Such ground-based stations 106 and 112 maythus serve as an interface between the balloon network and the Internet,a cellular service provider's network, and/or other types of networks.Variations on this configuration and other configurations ofground-based stations 106 and 112 are also possible.

2a) Mesh Network Functionality

As noted, balloons 102A to 102F may collectively function as a meshnetwork. More specifically, since balloons 102A to 102F may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may functionas a node of the mesh network, which is operable to receive datadirected to it and to route data to other balloons. As such, data may berouted from a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ variousrouting techniques and self-healing algorithms. In some embodiments, aballoon network 100 may employ adaptive or dynamic routing, where alightpath between a source and destination balloon is determined andset-up when the connection is needed, and released at a later time.Further, when adaptive routing is used, the lightpath may be determineddynamically depending upon the current state, past state, and/orpredicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102F move relative to one another and/or relative to the ground.Accordingly, an example balloon network 100 may apply a mesh protocol toupdate the state of the network as the topology of the network changes.For example, to address the mobility of the balloons 102A to 102F,balloon network 100 may employ and/or adapt various techniques that areemployed in mobile ad hoc networks (MANETs). Other examples are possibleas well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical components involved in thephysical routing of optical signals. Thus, in a transparentconfiguration with optical switching, signals travel through a multi-hoplightpath that is entirely optical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102F may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.Additionally, network configurations are possible that include routingpaths with both transparent and opaque sections.

In a further aspect, balloons in an example balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath. Alternatively, opticalwavelength conversion could take place at only selected hops along thelightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exampleballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for maintaining a particularquality of service (QoS) may be employed when determining a lightpath.Other techniques are also possible.

2b) Station-Keeping Functionality

In an example embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Fmaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102F may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such cases, a given balloon102A to 102F may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, example embodiments may involve topologies where balloonsare distributed more or less densely in certain areas, for variousreasons. As an example, to help meet the higher bandwidth demands thatare typical in urban areas, balloons may be clustered more densely overurban areas. For similar reasons, the distribution of balloons may bedenser over land than over large bodies of water. Many other examples ofnon-uniform topologies are possible.

In a further aspect, the topology of an example balloon network may beadaptable. In particular, station-keeping functionality of exampleballoons may allow the balloons to adjust their respective positioningin accordance with a change in the desired topology of the network. Forexample, one or more balloons could move to new positions to increase ordecrease the density of balloons in a given area. Other examples arepossible.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

2c) Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a block diagram illustratinga balloon-network control system, according to an example embodiment. Inparticular, FIG. 2 shows a distributed control system, which includes acentral control system 200 and a number of regional control-systems 202Ato 202B. Such a control system may be configured to coordinate certainfunctionality for balloon network 204, and as such, may be configured tocontrol and/or coordinate certain functions for balloons 206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via a number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 206A, 206F, and 206I are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 206A, 206F, and 206I via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, only some of balloons 206A to 206I areconfigured as downlink balloons. The balloons 206A, 206F, and 206I thatare configured as downlink balloons may relay communications fromcentral control system 200 to other balloons in the balloon network,such as balloons 206B to 206E, 206G, and 206H. However, it should beunderstood that in some implementations, it is possible that allballoons may function as downlink balloons. Further, while FIG. 2 showsmultiple balloons configured as downlink balloons, it is also possiblefor a balloon network to include only one downlink balloon, or possiblyeven no downlink balloons.

Note that a regional control system 202A to 202C may in fact just be aparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g., such as ground-based station112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may beimplemented in conjunction with other types of ground-based stations(e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all of the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all of the balloons 206A to 206I. The topologymay provide a picture of the current optical links that are available inballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralizedcontrol, with regional control systems 202A to 202C coordinatingcommunications between a central control system 200 and a balloonnetwork 204. Such an arrangement may be useful to provide centralizedcontrol for a balloon network that covers a large geographic area. Insome embodiments, a distributed arrangement may even support a globalballoon network that provides coverage everywhere on earth. Of course, adistributed-control arrangement may be useful in other scenarios aswell.

Further, it should be understood that other control-system arrangementsare also possible. For instance, some implementations may involve acentralized control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network maybe shared by a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control systems. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

As an example, each balloon A may receive distance information d₁ tod_(k) with respect to each of its k closest neighbors. Each balloon Amay treat the distance to each of the k balloons as a virtual springwith vector representing a force direction from the first nearestneighbor balloon i toward balloon A and with force magnitudeproportional to d_(i). The balloon A may sum each of the k vectors andthe summed vector is the vector of desired movement for balloon A.Balloon A may attempt to achieve the desired movement by controlling itsaltitude.

Alternatively, this process could assign the force magnitude of each ofthese virtual forces equal to d_(i)×d_(i), for instance. Otheralgorithms for assigning force magnitudes for respective balloons in amesh network are possible.

In another embodiment, a similar process could be carried out for eachof the k balloons and each balloon could transmit its planned movementvector to its local neighbors. Further rounds of refinement to eachballoon's planned movement vector can be made based on the correspondingplanned movement vectors of its neighbors. It will be evident to thoseskilled in the art that other algorithms could be implemented in aballoon network in an effort to maintain a set of balloon spacingsand/or a specific network capacity level over a given geographiclocation.

2d) Example Balloon Configuration

Various types of balloon systems may be incorporated in an exampleballoon network. As noted above, an example embodiment may utilizehigh-altitude balloons, which could typically operate in an altituderange between 18 km and 25 km. FIG. 3 shows a high-altitude balloon 300,according to an example embodiment. As shown, the balloon 300 includesan envelope 302, a skirt 304, a payload 306, and a cut-down system 308,which is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of materials including metalized Mylaror BoPet. Additionally or alternatively, some or all of the envelope 302and/or skirt 304 may be constructed from a highly-flexible latexmaterial or a rubber material such as chloroprene. Other materials arealso possible. Further, the shape and size of the envelope 302 and skirt304 may vary depending upon the particular implementation. Additionally,the envelope 302 may be filled with various different types of gases,such as helium and/or hydrogen. Other types of gases are possible aswell.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein. Thus, processor 312, in conjunctionwith instructions stored in memory 314, and/or other components, mayfunction as a controller of balloon 300.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include an optical communication system 316,which may transmit optical signals via an ultra-bright LED system 320,and which may receive optical signals via an optical-communicationreceiver 322 (e.g., a photodiode receiver system). Further, payload 306may include an RF communication system 318, which may transmit and/orreceive RF communications via an antenna system 340.

The payload 306 may also include a power supply 326 to supply power tothe various components of balloon 300. The power supply 326 couldinclude a rechargeable battery. In other embodiments, the power supply326 may additionally or alternatively represent other means known in theart for producing power. In addition, the balloon 300 may include asolar power generation system 327. The solar power generation system 327may include solar panels and could be used to generate power thatcharges and/or is distributed by the power supply 326.

The payload 306 may additionally include a positioning system 324. Thepositioning system 324 could include, for example, a global positioningsystem (GPS), an inertial navigation system, and/or a star-trackingsystem. The positioning system 324 may additionally or alternativelyinclude various motion sensors (e.g., accelerometers, magnetometers,gyroscopes, and/or compasses).

The positioning system 324 may additionally or alternatively include oneor more video and/or still cameras, and/or various sensors for capturingenvironmental data.

Some or all of the components and systems within payload 306 may beimplemented in a radiosonde or other probe, which may be operable tomeasure, e.g., pressure, altitude, geographical position (latitude andlongitude), temperature, relative humidity, and/or wind speed and/orwind direction, among other information.

As noted, balloon 300 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application. The optical communicationsystem 316 and other associated components are described in furtherdetail below.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in the envelope 302.

In an example embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The bladder 310could be an elastic chamber configured to hold liquid and/or gas.Alternatively, the bladder 310 need not be inside the envelope 302. Forinstance, the bladder 310 could be a rigid bladder that could bepressurized well beyond neutral pressure. The buoyancy of the balloon300 may therefore be adjusted by changing the density and/or volume ofthe gas in bladder 310. To change the density in bladder 310, balloon300 may be configured with systems and/or mechanisms for heating and/orcooling the gas in bladder 310. Further, to change the volume, balloon300 may include pumps or other features for adding gas to and/orremoving gas from bladder 310. Additionally or alternatively, to changethe volume of bladder 310, balloon 300 may include release valves orother features that are controllable to allow gas to escape from bladder310. Multiple bladders 310 could be implemented within the scope of thisdisclosure. For instance, multiple bladders could be used to improveballoon stability.

In an example embodiment, the envelope 302 could be filled with helium,hydrogen or other lighter-than-air material. The envelope 302 could thushave an associated upward buoyancy force. In such an embodiment, air inthe bladder 310 could be considered a ballast tank that may have anassociated downward ballast force. In another example embodiment, theamount of air in the bladder 310 could be changed by pumping air (e.g.,with an air compressor) into and out of the bladder 310. By adjustingthe amount of air in the bladder 310, the ballast force may becontrolled. In some embodiments, the ballast force may be used, in part,to counteract the buoyancy force and/or to provide altitude stability.

In other embodiments, the envelope 302 could be substantially rigid andinclude an enclosed volume. Air could be evacuated from envelope 302while the enclosed volume is substantially maintained. In other words,at least a partial vacuum could be created and maintained within theenclosed volume. Thus, the envelope 302 and the enclosed volume couldbecome lighter than air and provide a buoyancy force. In yet otherembodiments, air or another material could be controllably introducedinto the partial vacuum of the enclosed volume in an effort to adjustthe overall buoyancy force and/or to provide altitude control.

In another embodiment, a portion of the envelope 302 could be a firstcolor (e.g., black) and/or a first material from the rest of envelope302, which may have a second color (e.g., white) and/or a secondmaterial. For instance, the first color and/or first material could beconfigured to absorb a relatively larger amount of solar energy than thesecond color and/or second material. Thus, rotating the balloon suchthat the first material is facing the sun may act to heat the envelope302 as well as the gas inside the envelope 302. In this way, thebuoyancy force of the envelope 302 may increase. By rotating the balloonsuch that the second material is facing the sun, the temperature of gasinside the envelope 302 may decrease. Accordingly, the buoyancy forcemay decrease. In this manner, the buoyancy force of the balloon could beadjusted by changing the temperature/volume of gas inside the envelope302 using solar energy. In such embodiments, it is possible that abladder 310 may not be a necessary element of balloon 300. Thus, invarious contemplated embodiments, altitude control of balloon 300 couldbe achieved, at least in part, by adjusting the rotation of the balloonwith respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). Thenavigation system may implement station-keeping functions to maintainposition within and/or move to a position in accordance with a desiredtopology. In particular, the navigation system may use altitudinal winddata to determine altitudinal adjustments that result in the windcarrying the balloon in a desired direction and/or to a desiredlocation. The altitude-control system may then make adjustments to thedensity of the balloon chamber in order to effectuate the determinedaltitudinal adjustments and cause the balloon to move laterally to thedesired direction and/or to the desired location. Alternatively, thealtitudinal adjustments may be computed by a ground-based orsatellite-based control system and communicated to the high-altitudeballoon. In other embodiments, specific balloons in a heterogeneousballoon network may be configured to compute altitudinal adjustments forother balloons and transmit the adjustment commands to those otherballoons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. The cut-down system 308 could include at leasta connector, such as a balloon cord, connecting the payload 306 to theenvelope 302 and a means for severing the connector (e.g., a shearingmechanism or an explosive bolt). In an example embodiment, the ballooncord, which may be nylon, is wrapped with a nichrome wire. A currentcould be passed through the nichrome wire to heat it and melt the cord,cutting the payload 306 away from the envelope 302.

The cut-down functionality may be utilized anytime the payload needs tobe accessed on the ground, such as when it is time to remove balloon 300from a balloon network, when maintenance is due on systems withinpayload 306, and/or when power supply 326 needs to be recharged orreplaced.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit does not need to be accessed on the ground. In yet other embodiments,in-flight balloons may be serviced by specific service balloons oranother type of service aerostat or service aircraft.

3. Balloon Network with Optical and RF Links Between Balloons

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. Generally, the optical links between super-nodeballoons may be configured to have more bandwidth than the RF linksbetween super-node and sub-node balloons. As such, the super-nodeballoons may function as the backbone of the balloon network, while thesub-nodes may provide sub-networks providing access to the balloonnetwork and/or connecting the balloon network to other networks.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.More specifically, FIG. 4 illustrates a portion of a balloon network 400that includes super-node balloons 410A to 410C (which may also bereferred to as “super-nodes”) and sub-node balloons 420 (which may alsobe referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF)communication system that is operable for packet-data communication overone or more RF air interfaces. Accordingly, each super-node balloon 410Ato 410C may include an RF communication system that is operable to routepacket data to one or more nearby sub-node balloons 420. When a sub-node420 receives packet data from a super-node 410, the sub-node 420 may useits RF communication system to route the packet data to a ground-basedstation 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use using high-power or ultra-bright LEDsto transmit optical signals over optical links 402, 404, which mayextend for as much as 100 miles, or possibly more. Configured as such,the super-nodes 410A to 410C may be capable of optical communications atdata rates of 10 to 50 GBit/sec or more.

A larger number of high-altitude balloons may then be configured assub-nodes, which may communicate with ground-based Internet nodes atdata rates on the order of approximately 10 Mbit/sec. For instance, inthe illustrated implementation, the sub-nodes 420 may be configured toconnect the super-nodes 410 to other networks and/or directly to clientdevices.

Note that the data speeds and link distances described in the aboveexample and elsewhere herein are provided for illustrative purposes andshould not be considered limiting; other data speeds and link distancesare possible.

In some embodiments, the super-nodes 410A to 410C may function as a corenetwork, while the sub-nodes 420 function as one or more access networksto the core network. In such an embodiment, some or all of the sub-nodes420 may also function as gateways to the balloon network 400.Additionally or alternatively, some or all of ground-based stations 430may function as gateways to the balloon network 400.

4. Controlling the Altitude of a Balloon Using a First Mode of Operationby Having an Envelope with a First Portion and a Second Portion, wherethe First Portion Allows More Solar Energy to be Transferred to Gaswithin the Envelope and Rotatable to Position a Desired Portion of theEnvelope in a Direction Facing the Sun During the Day.

In an embodiment, as shown in FIG. 5A, a balloon 500 is shown, with FIG.5B showing a view of balloon 500 from above. The buoyancy of the balloon500 (and thus the altitude of the balloon) may be controlled byadjusting the temperature of the gas within envelope 502. As thetemperature of the gas within envelope 502 increases, the relativedensity of the gas within the envelope 502 decreases and the volume ofthe gas increases, which may result in a more buoyant (or upward) forceon the balloon 500, which may cause the altitude of the balloon toincrease. Similarly, as the temperature of the gas within envelope 502decreases, the relative density of the gas within envelope 502 increasesand the volume of the gas decreases, which may result in a less buoyant(or upward) force on the balloon 500, which may cause the altitude ofthe balloon to decrease. Thus, the altitude of balloon 500 may becontrolled by increasing or decreasing the temperature of the gas withinthe envelope 502.

During the day, the temperature of the gas within the envelope of theballoon may be controlled using a first mode of operation by controllingthe amount of solar energy that is absorbed by the gas within theenvelope. In particular, white surfaces, or lightly colored surfaces,absorb less solar energy than black surfaces, or darkly coloredsurfaces. Thus, the amount of solar energy absorbed by the gas withinenvelope 502, and thus the temperature of the gas, may be controlled ifthe absorptive/reflective properties of the surface of the envelope 502that is facing the sun are adjustable. Accordingly, theabsorptive/reflective properties of the surface of the envelope 502 maybe adjusted, or varied, by rotating an envelope 502 having a firstportion 502 a that allows for less transfer of solar energy to gaswithin the envelope (e.g., via decreased absorption and/or increasedreflection of sunlight), than a second portion 502 b of the envelope.

For example, a first portion of the envelope 502 a could be coloredwhite, or some other light color, which reflects more solar energy thana dark colored surface to help prevent the temperature of the gas withinthe envelope 502 from rising. A second portion of the envelope 502 bcould be colored black, or some other dark color, which absorbs moresolar energy than a lightly colored surface to allow more solar energyto be absorbed by the gas within the envelope 502, causing thetemperature of the gas within the envelope 502 to rise.

Alternatively, but operating on similar principles, the first portion ofthe envelope 502 a could be opaque or reflective, thereby preventingsunlight from passing into the envelope 502, to help prevent thetemperature of the gas within envelope 502 from rising. The secondportion of the envelope 502 b could be translucent, or transmissive,allowing sunlight to pass through the second portion of envelope 502 band thereby more solar energy to be absorbed by the gas within theenvelope 502, to cause the temperature of the gas within the envelope502 to rise.

Furthermore, alternately, or in addition to varying the absorptive orreflective properties of the portions of the balloon envelope to controlthe amount of solar energy entering the balloon envelope, it is alsopossible to provide a non-symmetrically shaped balloon such that a firstportion of the balloon may be oriented towards the sun that allows formore solar energy to be absorbed by the gas within the envelope thanwhen a second portion of the balloon is oriented towards the sun.

For example, in FIG. 8A, balloon 1500 is shown having an envelope 1502having a first portion 1502 a that has a large circular surface areathat allows for more solar energy to be absorbed by the gas within theenvelope 1502 than second portion 1502 b of envelope 1502 shown in FIG.8B. FIG. 8B shows balloon envelope 1502 after it has been rotated 90degrees from the position shown in FIG. 8A. By choosing which portion(1502 a or 1502 b) of the non-symmetrically shaped balloon envelope toorient towards the sun, differential heat may be brought into theballoon. By rotating or turning the balloon 1500 relative to the sun,substantial heating or cooling may be caused by presenting more or lessof the surface of the envelope to the sun, without regard to whatmaterials is used for the first portion 1502 a or second portion 1502 b.Of course, a non-symmetrically shaped balloon may be used with a balloonhaving the same material used for its entire envelope surface area, ormay be used in conjunction with a first portion of the balloon havingdifferent reflective, transmissive, or emissive properties than a secondportion of the balloon.

Referring back to FIGS. 5A and 5B, by controlling whether portion 502 aor 502 b of the envelope 502 is facing the sun, the temperature of thegas within the envelope 502 of balloon 500 may be controlled. Asdiscussed in more detail below, balloon 500 may be equipped with theability to rotate the envelope 502 so that the first portion of theenvelope 502 a or the second portion of the envelope 502 b is positionedfacing the sun. Where it is desired to increase the altitude of balloon500, the first portion of the envelope 502 a that allows for more solarenergy to be absorbed by the gas within the envelope 502 may bepositioned facing the sun to increase the temperature of the gas withinenvelope 502 (and increase the altitude of the balloon 500). Similarly,where it is desired to decrease the altitude of balloon 500, the secondportion of the envelope 502 b that allows for less solar energy to beabsorbed by the gas within the envelope 502 may be positioned facing thesun to decrease the temperature of the gas within the envelope 502 (anddecrease the altitude of the balloon 500).

Similarly, referring back to FIGS. 8A and 8B, by controlling whetherportion 1502 a or 1502 b of the envelope 1502 is facing the sun, thetemperature of the gas within the envelope 1502 of balloon 1500 may becontrolled. Balloon 1500 may be equipped with the ability to rotate theenvelope 1502 so that the first portion of the envelope 1502 a or thesecond portion of the envelope 1502 b is positioned facing the sun.Where it is desired to increase the altitude of balloon 1500, the firstportion of the envelope 1502 a that allows for more solar energy to beabsorbed by the gas within the envelope 1502 may be positioned facingthe sun to increase the temperature of the gas within envelope 1502 (andincrease the altitude of the balloon 1500). Similarly, where it isdesired to decrease the altitude of balloon 1500, the second portion ofthe envelope 1502 b that allows for less solar energy to be absorbed bythe gas within the envelope 1502 may be positioned facing the sun todecrease the temperature of the gas within the envelope 1502 (anddecrease the altitude of the balloon 1500).

It will be appreciated that it may be desirable to have a certain amountof the first or second (or even third or more portions) of the envelopefacing the sun. Thus, for example, it may be preferred to have 100% ofthe first portion of the envelope facing the sun, and 0% of the secondportion of the envelope facing the sun, or vice versa. Alternately, itmay be desired to have a preferred ratio of 30% of the first portion ofthe envelope and 70% of the second portion of the envelope facing thesun.

FIGS. 5A and 5B show a simplified scenario making the assumption thathalf of the balloon surface is exposed to the sun. However, as shown inFIGS. 6A and 6B, in balloon 1400, envelope portion 1402 a allows moresolar energy to be absorbed by the gas within the envelope 1402 thanenvelope portion 1402 b. Envelope portion 1402 a covers an area W, andin certain times of the day, e.g., when the sun is directly overhead,only a portion W′ of area W is directly exposed to sunlight. Similarly,envelope portion 1402 b allows less solar energy to be absorbed by thegas within the envelope 1402 than envelope portion 1402 a. Envelopeportion 1402 covers an area B, and at certain times of the day, only aportion B′ of area B is directly exposed to sunlight.

Assuming area W has an energy transmission factor WT and area B has anenergy transmission factor BT, and the surface area of the sun-exposedarea of W is W′ and the surface area of the sun-exposed area B is B′,the total energy to be absorbed by the gas within the balloon envelopemay be governed by the equations EnergyTotal=(W′×WT)+(B′×BT). Thus, theamount of energy transferred to the gas within the envelope 1402 may beviewed as a function of area W′ and B′ that is directly exposed to thesun. By rotating the balloon envelope 1402 so that the area of W′ isincreased (and therefore the area B′ is decreased), the amount of solarenergy transferred to the gas within envelope 1402 may be increased.Conversely, if it is desired to decrease the amount of energy absorbedthe gas within the envelope 1402, then the balloon envelope 1402 may berotated so that the area W′ is decreased (and therefore the area B′ isincreased).

The above equation for EnergyTotal may also be simplified in that itassumes that the energy transmission factors WT is constant acrosssun-exposed area W′ and that energy transmission factor BT is alsoconstant across sun-exposed area B′. However, the energy transmissionfactors WT and BT might vary across the surface of the envelope based onthe angle of incidence at which the sunlight hits the envelope at agiven point. In addition, the amount of solar energy transferred to gasin the envelope may be a function of the shape and size of the surfacearea that faces the sun, the size and shape of B′ and W′, the positionand/or location of the sun relative to the envelope, the intensity ofsunlight (which may be a function of the time of day, the month, theyear), and/or the absorptive, reflective, and/or refractive propertiesof the materials with which B and W are constructed.

Nonetheless, the amount of solar energy absorbed or reflected by theballoon envelope may be controlled and/or adjusted by controlling and/oradjusting the amount of the portions of the balloon envelope that arefacing the sun. In this manner, the energy absorption of the gas or airwithin the balloon may be controlled in a continuous fashion by alteringthe ratios of the portions of the balloon envelope facing the sun.

FIGS. 5 and 5A show sharp dividing lines between the different portionsof the envelope. However, it will appreciated that the division betweenthe first and section portions of the envelope could be gradual,allowing for a continuously decreasing amount of solar energy absorbedby the gas within the envelope as the darker or more transmissiveportion of the envelope is rotated away from a position facing the sunto a position where the lighter or more opaque or reflective portion ofthe envelope is positioned facing the sun. Thus, with a gradual changebetween the first and second portions of the envelope, as the envelopeis slowly rotated, the amount of solar energy that may be absorbed bythe gas within the envelope may be slowly reduced. The portions of theballoon envelope could be made of materials that either absorb light orreflect light so as to change the temperature (and therefore thepressure and density of the gas) on the inside of the balloon, as wellas materials that change their elasticity and expand and/or contractwhen they, or the gas within them, or heated and/or cooled.

In addition, the size and the shape of the balloon could be modified tofurther allow for a more clear distinction between the first and secondportions of the envelope. For example, the envelope of the balloon couldhave a generally rectangular shape with two oppositely disposed majorsurfaces corresponding to the first and second portions of the envelope.

The balloon 500 shown in FIGS. 5A and 5B, or balloon 1500 shown in FIGS.8A and 8B may, but is not required to, further include a bladder, likethe bladder 310 depicted in FIG. 3. The bladder may be used to act as atype of ballast to further control the altitude of the balloon 500 or1500. As the bladder is filled with more air, the density of the gaswithin the envelope increases resulting in a decrease in the buoyant,upward force of the balloon, which also results in a decrease in thealtitude of the balloon. Similarly, to increase the buoyant, upwardforce of the balloon and increase the altitude of the balloon, the airmay be removed, or bled, from the bladder, resulting in a lower densityof the gas in the envelope and a higher buoyant, upward force of theballoon, which results in an increase in the altitude of the balloon.

In addition, there are also alternative ways of using the naturalenvironment and/or natural temperature changes to control thetemperature of the gas and/or air within the balloon (in the balloonenvelope or bladder) to control or change the altitude of the balloon.For example, one could make the balloon fairly thermally insulated,e.g., with a low emissivity, and then include a heat sink (which couldtake the form of a metal fin, or a fin made of a thermally conductivematerial such as Beryllium Copper) that is extendable and/or retractablefrom the balloon such that the fin could be positioned below the balloonand thermally coupled to the gas within the balloon (via a rod, forexample). In this manner, when it is desired to cool the gas within theballoon (in the bladder or envelope) more quickly, the heat sink couldbe deployed and the metal fin extended into the atmosphere where heatfrom within the balloon may be transferred to the atmosphere. Similarly,when it desired to cool the air or gas within the balloon more slowly,the heat sink or fin could be retracted so that less heat is transferredfrom the gas or air within the balloon to the atmosphere. Thus, the heatsink or fin may be extended when it is desired to cool the air or gaswithin the balloon more quickly, and the heat sink or fin may beretracted when it is desired to cool the air or gas within the balloonmore slowly.

The rotation of the envelope may be accomplished by using an offset fanor fans positioned on and extending from one of the components of theballoon 500. The further the fan is placed from the center of mass ofthe balloon, the greater the rotational force for rotating the envelopeof the balloon. The fan or fans may be attached to a retractable arm orsupport when not needed for operation.

In addition, a directional spigot of compressed air, or compressed airdirected towards a thrust plate or thrust deflector (retractable and/oradjustable if desired) positioned on and extending from a component ofthe balloon 500 could also be used to achieve the desired rotation ofthe envelope. The further the directional spigot or compressed air isplaced from the center of mass of the balloon, the greater therotational force for rotating the envelope of the balloon. A fin or wingthat is manoeuvrable may be used to rotate, or control the rotation, ofthe balloon.

In some applications, it may be desirable to have the envelope 502 ofthe balloon 500 rotatable about the payload, the cut-down, or the skirt.For example, the envelope 502 may be rotatably connected using a gimbalsupport, or spherical roller bearing, thereby allowing three degrees offreedom, i.e., roll, pitch, and yaw at the point of connection. Inaddition, the rotatable connection could be made using any of a varietyof bearings, including a plain bearing, a friction bearing, or rollerbearing, or even an air bearing.

The rotation of the envelope 502 may be controlled by a motor, orservomotor. The rotation of the envelope 500 may be further controlledby an indexing mechanism. Such an indexing mechanism could include aratchet and pawl indexing mechanism that allows for a toothed ratchet orgear to rotate freely in one direction, but that is prevented fromrotating in the opposite direction by a pawl, where the pawl could bespring loaded. A roller ratchet or notched wheel could also be used forindexing.

With reference to FIG. 3, the envelope of the balloon could becontrolled to rotate a desired portion of the envelope towards the sun.

The positioning of the desired portion of the envelope towards the suncould be performed by the balloon that the envelope is attached to, forinstance using processor 312 and memory 314 to control rotatableconnection of the envelope. Alternatively, the positioning of thedesired portion of the balloon could be controlled remotely by anotherballoon or ground- or space-based station.

Once under local or remote control, positioning of the envelope could beadjusted as the sun moved to point the desired portion of the envelopetowards the sun. In other words, adjustments could be performed with aneffort to maintain the positioning of the desired portion of theenvelope towards the sun. Or the positioning of the desired portion ofthe envelope could be continuously adjusted to account for the continualmovement of the sun.

In any event, during times when the sun is out, it may be possible tocontrol, at least in part, the altitude of the balloon by rotating theballoon so that desired portions of the envelope are facing the sun,thereby controlling of the amount of solar energy that is absorbed bythe gas within the envelope of the balloon. Using solar energy tocontrol the altitude of the balloon may be advantageous because lessenergy may be consumed rotating the balloon into proper positionrelative to the sun, than using other methods of altitude controlincluding inflating/deflating the balloon envelope or bladder, orburning hydrogen to heat the gas within the balloon.

5. Using a Second Mode of Operation for Altitude Control

At night time, when the sun is down, it may no longer be possible to usedirect solar energy and rotation of the balloon envelope to control thealtitude of the balloon. Therefore, a second mode for controllingaltitude should be available during the night. A second mode ofoperation used to control the altitude of the balloon at night is byintroducing additional lifting gas into the balloon envelope or bladder.In this manner, gas may be pumped into or out of the balloon envelope orbladder to control the altitude of the balloon at night. Altimeters orother devices may be used determine the altitude and/or rate of descentand provide for switching from a first mode of altitude control usingsolar energy, to a second mode of altitude control usinginflation/deflation of the balloon envelope or bladder with gas, or somecombination thereof. Of course, at certain times of the day, it may bedesirable to use the first mode of operation for altitude control, thesecond mode of altitude control, or the first mode and second mode ofoperation for altitude control at the same time.

Furthermore, in order to harness energy to provide for altitude controlat night, the payload may include one or more solar cells to storeenergy that can be used for altitude control during the night. Forexample, solar energy stored during the day may be used to control thealtitude of the balloon by pumping gas into, or out of, the envelope ofthe balloon, or the bladder of the balloon.

During the second mode of altitude control, the balloon envelope mayneed to expand to allow the gas to become less dense and to provide amore buoyant upward force. As shown in FIG. 7, during the night forexample, the balloon envelope 902 of balloon 900 may expand. Forexample, the balloon envelope 902 may expand from an envelope size 902Dto an envelope size 902E. Similarly, the bladder 910 of balloon 910 mayalso expand as gas is pumped into the bladder from, as an example,bladder size 910A to bladder size 910B, and even to bladder size 910C.

When the sun comes back up the following morning, it may desirable toswitch back to the first mode of controlling the balloon altitude, usingrotation of the balloon envelope to properly position the balloonenvelope in relation to the sun and to adjust the temperature of the gaswithin the balloon envelope as desired. It should be clear that thefirst mode of altitude control and the second mode of altitude controldiscussed above are not two different mutually exclusive modes. Duringthe day, it may be desirable to use the first mode of altitude controlas much as possible, but this may need to be augmented by also using thesecond mode of altitude control. For example, from 11 am to 1 pm, whenthe sun is mostly directly above the balloon, the second mode ofaltitude control may need to be mostly used. Also, even in the day, theheat from the sun used in the first mode of altitude control may notprovide as much vertical travel as desired so it may need to be to beaugmented even at 3 pm (which is about the best time for this) with thepump used in the second mode of altitude control.

Accordingly, when inflating the balloon envelope for altitude control,it may be desirable to allow the exterior shape of the envelope toexpand as the temperature of the gas within the envelope is increased,and to have the exterior shape return to its normal shape when thetemperature of the gas within the envelope is decreased. The use ofmemory metal may be used for the exterior of the balloon envelope toallow the balloon to expand when the temperature of the gas within theenvelope is increased, and return to its former exterior shape when thetemperature of the gas within the envelope is decreased. Thus, theexterior shape of the envelope may change back and forth from its normalexterior shape to an expanded shape.

FIG. 9 shows a method 1200 that is provided that includes the step 1202of determining a location of a balloon with respect to the sun, whereinthe balloon has an envelope with a gas contained within the envelope anda payload connected to the envelope, and the envelope has a firstportion that has a first absorptive or reflective property with respectto allowing solar energy to be transferred to the gas within theenvelope, and a second portion that has a second absorptive orreflective property that is different from the first absorptive orreflective property. The method 1200 further includes the step 1204 ofrotating the envelope of the balloon to position the first portion orsecond portion of the envelope facing the sun. The method 1200 may alsoprovide an additional mode of altitude control by including the step1206 of admitting or releasing gas or air into a bladder positionedwithin the envelope to raise or lower the altitude of the balloon, oradmitting or releasing gas or air into the balloon envelope to raise orlower the altitude of the balloon. Other techniques known in the art toproperly position a desired portion of the envelope towards the sun maybe reasonably used within the context of the disclosure.

6. A Non-Transitory Computer Readable Medium with Instructions toControl the Positioning of a Desired Portion of the Envelope Towards theSun.

Some or all of the functions described above and illustrated in FIGS. 3,5A, 5B, 6A, 6B, 7, 8A, and 8B may be performed by a computing device inresponse to the execution of instructions stored in a non-transitorycomputer readable medium. The non-transitory computer readable mediumcould be, for example, a random access memory (RAM), a read-only memory(ROM), a flash memory, a cache memory, one or more magnetically encodeddiscs, one or more optically encoded discs, or any other form ofnon-transitory data storage. The non-transitory computer readable mediumcould also be distributed among multiple data storage elements, whichcould be remotely located from each other. The computing device thatexecutes the stored instructions could be a computing device, such asthe processor 312 illustrated in FIG. 3. Alternatively, the computingdevice that executes the stored instructions could be another computingdevice, such as a server in a server network, or a ground-based station.

The non-transitory computer readable medium may store instructionsexecutable by the processor 312 to perform various functions. Thefunctions could include the determination of a location of a firstballoon, and the positioning of a portion of the envelope of the balloonin relation to the sun. The functions could also include pumping gas orair into or out of the balloon envelope or bladder to control thealtitude of the balloon during the night, or other desired times.

CONCLUSION

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. While various aspects and embodiments have beendisclosed herein, other aspects and embodiments will be apparent tothose skilled in the art. The various aspects and embodiments disclosedherein are for purposes of illustration and are not intended to belimiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A balloon, comprising: an envelope; a payloadpositioned beneath the envelope, wherein the envelope comprises a firstportion and a second portion, wherein the first portion allows moresolar energy to be transferred to gas within the envelope than thesecond portion; and a control system that is configured to cause theballoon to operate using a first mode in which altitudinal movement ofthe balloon is caused, at least in part, by rotating the envelope tochange an amount of the first portion that faces the sun and an amountof the second portion that faces the sun; wherein the control system isfurther configured, responsive to not attaining a desired altitude orrate of descent or ascent, to cause the balloon to operate using asecond mode in which altitudinal movement of the balloon is caused, atleast in part, by moving a lifting gas or air into or out of theenvelope.
 2. The balloon of claim 1, wherein altitudinal movement of theballoon while operating in the second mode is caused, at least in part,by moving the lifting gas or air into or out of a bladder within theenvelope.
 3. The balloon of claim 1, wherein the control system causesthe balloon to operate using the first mode and the second mode at thesame time.
 4. The balloon of claim 1, wherein altitudinal movement ofthe balloon in the first mode is further caused by moving a lifting gasor air into or out of the envelope.
 5. The balloon of claim 1, whereinthe lifting gas or air is moved into a bladder within the envelope. 6.The balloon of claim 1, wherein one or more solar cells are positionedwithin the payload to store energy for altitudinal movement of theballoon when it operates using the first and/or second mode.
 7. Theballoon of claim 1, wherein the second mode of altitude control isprovided where a lifting gas or air is moved into or out of the balloonenvelope to control the altitude of the balloon.
 8. The balloon of claim1, wherein the second mode of altitude control is provided where alifting gas or air is moved into or out of a bladder within the balloonenvelope to control the altitude of the balloon.
 9. The balloon of claim1, wherein during the second mode of altitude control, the envelope ofthe balloon may expand from a first size to a second shape.
 10. Theballoon of claim 9, wherein the balloon envelope includes memory metalto return the balloon to the first size after it has been expanded. 11.The balloon of claim 1, wherein the envelope is non-symmetrical in shapesuch that the first portion has a surface area that is greater than asurface area of the second portion.
 12. The balloon of claim 11, whereinmore solar energy is transferred to gas within the envelope when thefirst portion of the balloon is facing the sun than when the secondportion of the balloon is facing the sun.
 13. The balloon of claim 1,wherein the first portion has different reflective, transmissive, and/oremissive properties than the second portion.
 14. The balloon of claim13, wherein the first portion has different reflective, transmissive,and/or emissive properties than the second portion when viewed in thethermal IR.
 15. A computer-implemented method, comprising: causing aballoon to operate using a first mode, wherein the balloon comprises anenvelope and a payload positioned beneath the envelope, wherein theenvelope comprises a first portion and a second portion, wherein thefirst portion allows more solar energy to be transferred to gas withinthe envelope than the second portion, and wherein operation in the firstmode comprises: causing altitudinal movement of the balloon via rotationof the envelope to change an amount of the first portion that faces thesun and an amount of the second portion that faces the sun; determiningthat an ambient light level is below a threshold; and responsivelycausing the balloon to operate using a second mode, wherein operation inthe second mode comprises: causing altitudinal movement of the balloonvia movement of a lifting gas or air into or out of the envelope. 16.The method of claim 15, wherein the causing altitudinal movement of theballoon via rotation of the envelope comprises operating one or morefans to rotate the envelope.
 17. The method of claim 15, wherein causingaltitudinal movement of the balloon via rotation of the envelopecomprises causing a directional spigot to release compressed air torotate the envelope.
 18. The method of claim 15, wherein the methodincludes operating the balloon using the first mode and the second modeat the same time.
 19. The method of claim 15, wherein the envelope isnon-symmetrical in shape such that the first portion has a surface areathat is greater than a surface area of the second portion.
 20. Themethod of claim 19, wherein more solar energy is transferred to gaswithin the envelope when the first portion of the balloon is facing thesun than when the second portion of the balloon is facing the sun. 21.The balloon of claim 15, wherein the first portion has differentreflective, transmissive, and/or emissive properties than the secondportion.
 22. The balloon of claim 21, wherein the first portion hasdifferent reflective, transmissive, and/or emissive properties than thesecond portion when viewed in the thermal IR.
 23. A non-transitorycomputer readable medium having stored therein instructions executableby a computing device to cause the computing device to perform functionscomprising: causing a balloon to operate using a first mode, wherein theballoon comprises an envelope and a payload positioned beneath theenvelope, wherein the envelope comprises a first portion and a secondportion, wherein the first portion allows more solar energy to betransferred to gas within the envelope than the second portion, andwherein operation in the first mode comprises: causing altitudinalmovement of the balloon via rotation of the envelope to change an amountof the first portion that faces the sun and an amount of the secondportion that faces the sun; determining that an ambient light level isbelow a threshold; and responsively causing the balloon to operate usinga second mode, wherein operation in the second mode comprises: causingaltitudinal movement of the balloon via movement of a lifting gas or airinto or out of the envelope.
 24. The non-transitory computer readablemedium of claim 23, wherein causing altitudinal movement of the balloonvia rotation of the envelope comprises operating one or more fans torotate the envelope.
 25. The non-transitory computer readable medium ofclaim 23, wherein causing altitudinal movement of the balloon viarotation of the envelope comprises causing a directional spigot torelease compressed air to rotate the envelope.